I am enjoying the tags in Calibre a lot. Ever since I figured out how to add cover art, it has been fun to browse my books and make lists. I have tags for source (Fictionwise, Kobo, Mobile Read etc) and for genre.

I also have a few special collections. One of them is a Canadian collection, of all-Canadian authors. The other I am calling the 'premium' collection for lack of a better word and it's basically my purchased books, but only the ones with pretty covers. So I can browse my purchased books without the amateurish covers of some of the multiformat freebies and without the list being over-taken by Star Trek books

I use the star system to show the book's status---4 stars is personal documents, 3 stars in 'on the Kindle right now' 2 stars is 'already read it in paper and have the ebook for re-reading later' and one star is 'already read.' So I can open any of my collections and at a glance see what's going on. I can sort by star and all the not-on-the-Kindle unread books go to the top and I can see what's good to add in my next sync. Once Kindle has collections, I will load every unread book on there and delete them off the Kindle as I read, like I did when I had the Sony, so I may re-assess the star ratings then.

Aside from the usual tags for genre, etc., I have a bunch of utility tags:

[processed] for the ones that I've gone over, fixed the metadata, found the cover, etc.
[main] for the ones that go to the Reader's main memory.
[card] for the ones that go to the SD card.
[DNU] for the ones that don't go to the Reader at all (primarily huge PDFs with teensy print).
[paid] for non-free books, so I don't accidentally mix one in with the Baen Free Library or something.

My most important saved search is the "NEW" one, which is just every book that doesn't have a [processed] tag. I import a bunch of books, pick that search, and I can then go through and work on all of them at once: fix their missing metadata, search for a cover, tag them by subject, etc. Once I'm satisfied with the metadata, I give that book a [processed] tag and it goes away, into the great sea of To-Be-Read.

I like the collections feature, but I hardly ever use the tag feature. In fact, whenever I get a book with tags, I delete them :-D That being said, I am finding that I am starting to use a TBR tag for all my unread books. That pile just keeps growing and growing.

I too love the cover art. I've spent several days worth of time going on Google Images and downloading the cover I like. Much easier for others to browse my collection if there is a picture to go with the title.

I'm also thinking of starting to write my own little review of a book in the comments section. Not sure if that will work out or not though.

During the voting period for the Nebula and Andre Norton Awards, I downloaded all the nominated stories and novels that authors and publishers made available (which included most, but not all, of the nominees), then tagged them in Calibre:

Nebula 2009 Short Story
Nebula 2009 Novelette
Norton 2009

and so on. Then I put them all on my Sony 700 and my PDA. It was very helpful in trying to at least sample everything, and read as much all the way through as possible. I quite enjoyed doing it this way.

(And the winners will be announced in just a week and a half from now, in Cocoa Beach, FL, just down the road from the Kennedy Space Center. If we are very, very lucky, we are going to see space shuttle Atlantis lift off, the day before the awards ceremony.)

Nothing terribly exciting. I only rate books once I have read them, and also use 0read0. I don't have any tag to show what is on my kindle, and so I tend to just upload the most recent books. I need to put some thought into this!